The speed of sound in soft tissues is usually assumed to be 1540 m/s
in medical pulse-echo ultrasound imaging systems. When the true speed
is different, the mismatch can lead to distortions in the acquired
images, and so reduce their clinical value. Previously we reported a
new method of sound-speed estimation in the context of image
deconvolution. Unlike most other sound-speed estimation methods, this
enables the use of unmodified ultrasound machines and a normal
scanning pattern. Our approach was validated for largely homogeneous
media with single sound speeds. In this article, we demonstrate that
sound speeds of dual-layered media can also be estimated through image
deconvolution. An ultrasound simulator has been developed for layered
media assuming that, for moderate speed differences, the reflection at
the interface may be neglected. We have applied our dual-layer
algorithm to simulations and in-vitro phantoms. The speed of the top
layer is estimated by our aforesaid method for homogeneous
media. Then, when the layer boundary position is known, a series of
deconvolutions are carried out with dual-layered point-spread
functions having different lower-layer speeds. The best restoration is
selected using a correlation metric. The error level for in-vitro
phantoms is found to be not as good as that of our single-speed
algorithm, but is comparable to other local speed estimation methods
where the data acquisition may not be as simple as in our proposed
method.

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